This invention relates to optical fibre sensing systems for monitoring and/or measuring temperatures or pressures distributed over a pre-determined path.
In our co-pending British Patent Application No. 8609733 (published under Ser. No. 2,207,236 on Jan. 25, 1989), to which attention is hereby directed, an optical fibre sensing system comprises an optical interferometer having measurement and reference optical paths in parallel relationship, the measurement path comprising an optical fibre extending over the path along which distributed temperature or pressure is to be measured, continuous wave light generating means producing coherent continuous wave light which propagates in one direction along the measurement and reference paths of the interferometer, pulse light generating means for producing light pulses which propagate along the measurement path only in the direction opposite to that in which the continuous wave light propagates to produce transient variations in the propagation constant (or its directly related phase change coefficient) of the optical fibre at points therealong according to the temperature or pressure at said points, and detector means for detecting the resultant output from the interferometer which will vary with time in dependence upon the temperature or pressure at distributed points along the measurement optical fibre path.